Medical delivery catheters are well known in the art of minimally invasive surgery for introduction of fluids and devices to sites inside a patient's body. For example, balloon dilation of luminal stenoses (e.g., in procedures such as angioplasty or balloon dilation of a bile duct), stent placement, and introduction of radio-opaque contrast fluids are common uses of catheters.
The most widely used form of angioplasty makes use of a dilation catheter having an inflatable balloon at its distal end. In coronary procedures, a hollow guide catheter or wire guide typically is used for guiding the dilation catheter through the vascular system to a position near the stenosis (e.g., to a coronary arterial lumen occluded by plaque). Using fluoroscopy, the physician guides the dilation catheter the remaining distance through the vascular system until a balloon is positioned to cross the stenosis. The balloon is then inflated by supplying pressurized fluid, through an inflation lumen in the catheter, to the balloon. Inflation of the balloon causes a widening of the lumen of the artery to reestablish acceptable blood flow through the artery. In some cases, a stent may be deployed with or instead of the balloon to widen and hold open the occluded arterial lumen.
Preferably a catheter used in endovascular lumens will have several physical characteristics. The profile and shaft size of the dilation catheter should be such that the catheter can reach and cross a very tight stenosis. Portions of the dilation catheter must also be sufficiently flexible to pass through a tight curvature or tortuous passageway, especially in a catheter adapted for use in the coronary arteries. The ability of a catheter to bend and advance effectively through the endovascular or other lumens is commonly referred to as the “trackability of the catheter.” Another important feature of a dilation catheter is its “pushability.” Pushability involves the transmission of longitudinal forces along the catheter from its proximal end to its distal end so that a physician can push the catheter through the vascular or other lumenal system and the stenoses. Effective catheters should be both trackable and pushable.
Two commonly used types of dilation catheters are referred to as “long-wire” catheters and “short-wire” catheters. A long-wire catheter is one in which a wire guide lumen is provided through the length of the catheter that is adapted for use with a wire guide that can first be used to establish the path to and through a stenosis to be dilated. The dilation catheter can then be advanced over the wire guide until the balloon on the catheter is positioned within the stenosis.
In short-wire catheters, the wire guide lumen may not extend the entire length of the catheter. In this type of catheter, the wire guide lumen may extend only from the distal end of the balloon to a point intermediate the distal and proximal ends of the catheter. This shorter lumen is the only portion of the catheter contacting the wire guide. It is sometimes desirable to exchange this first catheter and/or balloon for a second catheter (e.g., to “exchange out” a balloon catheter, and then “exchange in” a stent-deployment catheter). The exchange is preferably executed by leaving the wire guide in place during removal of the first catheter and using it as a guide for the second catheter. The first catheter is withdrawn or otherwise removed over the wire guide, and then a second catheter is introduced over the wire guide.
Short-wire catheters are often easier to exchange than catheters having the wire guide lumen extending the entire length of the catheter. This is because the wire guide need not be as long as a “long wire” configuration, which requires that a length of the wire guide extending outside the patient's body be longer than the portion of the catheter extending over the long wire guide in order for a doctor or assistant to maintain a grasp on the wire guide (to avoid undesired movement or displacement thereof). The short wire guide configuration catheters also create less friction during mounting and exchange operations due to the shorter wire guide lumen, leading to a reduced likelihood of displacing the wire guide.
Catheters for use in endovascular lumens typically require a variation in physical properties along different portions thereof. For example, a certain degree of stiffness is required for pushability and trackability near the proximal end while distal end requires a great deal of flexibility. A catheter having uniform properties throughout its length poses disadvantages in that it is likely to be too proximally flexible or too distally stiff. As a result, most catheter shafts (especially endovascular catheters) are made from multiple materials along the shaft length. For example, a catheter shaft may have a stiff proximal portion made of metal hypotube, a middle portion made of a stiff plastic, and a distal portion made of a more flexible plastic. This combination of materials poses problems of cost and efficiency in construction, and the junctions provide problematic possibilities for structural failure (such as binding, kinking, or even separation) as well as requiring specialized connection means. In another example, a catheter shaft may be made of plastic for a major part of its length, but have a stiffening wire disposed through a significant portion of that length to enhance stiffness. Some long wire catheters rely almost wholly on placement of a wire guide therethrough to retain the needed stiffness, which presents the problems of length and unwieldiness discussed above. In contrast, the proximal sections of short wire catheters must have adequate stiffness independent of the wire guide.